Memory cells are common constituents of integrated circuitry. An individual memory cell comprises a device that exists in two or more stable memory states. The act of “writing” to the device comprises placing the device into a desired memory state; and the act of “reading” the device comprises determination of which of the memory states the device is in.
The writing to the device may comprise imparting a programming voltage to the device, with the programming voltage being a voltage sufficient to cause the device to change from one memory state to another. The reading of the device may comprise measurement of an electrical parameter influenced by the memory state of the device, such as, for example, measurement of current passing through the device. It can be desired that the reading be conducted under conditions which do not alter the memory state of the device, so that the reading operation does not “write” to the device.
One way of avoiding undesired alteration of the memory state of a memory device during a reading operation is to conduct the reading at a voltage much less than the programming voltage. However, differences between the memory states of memory devices may become larger, and thus more easily measured, as voltages on the devices are increased. Thus, the reading of a memory device may comprise a trade-off between a desire to read the device accurately and quickly, and a desire to avoid alteration of the memory state of the device during the reading operation.
It would be desirable to develop new methods for reading memory devices which enable the devices to be read quickly and accurately.